package nbcb;

import java.util.Scanner;

public class C {
    public static void main(String[] args) {
        Scanner input=new Scanner(System.in);
        while(input.hasNext()) {
            double n=input.nextDouble();
            double m=input.nextDouble();
            double x=input.nextDouble();
            double y=input.nextDouble();
            double sum;
            sum=Math.sqrt((n-x)*(n-x)+(m-y)*(m-y));
            System.out.printf("%.2f\r\n",sum);
        }
    }
}
